QCT bone mineral density responses to 1 year of oral bisphosphonate after total knee replacement for knee osteoarthritis

Bone mineral density (BMD) declined in more than half (53.7%) of post-total knee arthroplasty (TKA) patients (44 of the 82) after 1 year of oral bisphosphonate treatment, and that this decline was significant in bilateral TKA patients. TKA has proven to be an extremely successful procedure in terms of improving ambulatory function. However, the effects of such improvements in ambulatory function and of bisphosphonate on axial BMD have not been established. The purpose of this study was to determine the effect of 1 year of oral bisphosphonate in postmenopausal patients that have undergone TKA and to identify factors related to BMD changes using lumbar spine quantitative computed tomography (QCT). Eighty-two postmenopausal women that underwent primary TKA for knee osteoarthritis and who received once-weekly oral alendronate 70 mg for 12 months after TKA were enrolled. The effect of 1 year of oral bisphosphonate treatment post-TKA and the factors related to general lumbar spine BMD changes by using QCT were determined. Some 53.7% of patients (44 of the 82) experienced an average lumbar spine QCT BMD decline of -6 mg/ml (range -15 to -0.5 mg/ml) after 1 year of oral bisphosphonate treatment, whereas the remaining 38 patients (46.3%) experienced an average increase of 6.8 mg/ml (range 0.6 to 15.7 mg/ml). Logistic and linear regression analysis showed that bilateral TKA was significantly related to a BMD decline (p < 0.05). Other factors, such as, age, body mass index, number of comorbidities, and Knee Society scores were not found to be significantly related to BMD response. BMD declined in more than half (53.7%) of the patients after bisphosphonate treatment, and that this decline was significant in bilateral TKA patients. We believe that reduced mobility during rehabilitation was probably responsible for these BMD reductions.